Christian Post believes his former friend Christian Brueckner came across Madeleine McCann by chance as she slept in her apartment before snatching her.
The 54-year-old is "convinced" the German paedophile took the three-year-old girl in May 2007 at Praia da Luz on the Algarve.
And Mr Post claimed Brueckner boasted of burgling holiday flats during chilling “night-crawls” around the Portuguese resort.
He told how the chief suspect in Madeleine’s disappearance had up to 100 passports from properties he raided. And he admitted he regrets not tipping off police about his crimes, but insisted he is willing to try to help bring him to justice over the missing British toddler.
German Mr Post, a talented musician and IT expert, became friends with Brueckner, 45, after the pair met in an Algarve bar in the early-2000s, The Mirror reports.
He initially believed his fellow countryman could not have been behind Madeleine’s kidnap and thought his criminality was limited to burglary.
But since discovering Brueckner had been convicted of child sex offences in his teens, Mr Post said it was now “so obvious” he snatched her.
He added: “Now I know about his paedophile past, his rapist past, I’m 100% certain it was him.
“I think he found her by chance and just took her on the spur of the moment.
“I think once you are a paedophile, there is a switch in your brain that cannot be turned off. If he saw a little girl asleep, alone in her apartment, he would definitely have taken her.
“Thinking about what he has done in the past makes me sick, it makes me want to vomit knowing I was hanging with him. If he is convicted of taking Madeleine I hope they lock him up and take away the key.” Mr Post was tracked down by the Mirror to a small town in Cambodia where he lives under an assumed name.
In his first ever interview he told how he and Brueckner would go to each other’s flats after they became friends.
Mr Post said he knew his new pal was on the “fringes” of crime but had no idea of the true scale until a later visit to his ramshackle farmhouse. He said: “I was sat in the living room and noticed piles of passports on the fireplace.
“There honestly must have been between 60 and 100 of them, neatly stacked up in three piles.
“He told me he got them on his ‘night-crawls’ in Praia da Luz, climbing on to balconies and through windows. It shows how many burglaries he must have done. He said he would go into rooms and take what he wanted. At the time I guessed he was talking about cash, jewellery, passports… but who knows?
“He would only do it at night, it was too risky being seen in the daylight.
“He also said he was trafficking a bit of weed to make cash. But there was absolutely no sign he was into children or anything like sexual crimes.
“Do I have regrets not telling the police about the passports at the time? I guess I do.
“But now I’m willing to go back to court, to face him again, and help convict him if they want me to.” Mr Post only found Brueckner had been convicted of child sex offences after reading about them in the press.
And we can reveal he has twice been interviewed by detectives investigating the suspect and Madeleine’s case.
Mr Post gave evidence against him at his 2019 trial for raping a pensioner in Praia da Luz in 2005, for which he is serving seven years in Germany.
He fell out with Brueckner in 2006 after the crook asked him to go to his house and clear out anything incriminating while he was in a Portimao prison for stealing petrol.
Mr Post found some porn films and binned them rather than take them to a friend’s house who had children. He said: “He thought I was stealing from him or something.”
The pair met briefly again in 2012 after Mr Post had returned to Germany to work on a Christmas market in Solingen near Dusseldorf.
But after moving to Cambodia in 2015, he was stunned when his brother rang three years later to say German detectives wanted to speak to him.
Mr Post added: “They said he was a suspect in the Madeleine case. I was absolutely shocked.”
He said he had never spoken about Brueckner publicly before over fears he would be linked to the Madeleine case. And he insisted he had nothing to do with any of the suspect’s crimes.
German prosecutors named Brueckner as a suspect in June 2020 and claim to have evidence that he abducted and killed her. He denies any involvement in the case.
Madeleine’s parents Kate, 54, and Gerry, 53, from Rothley, Leics, continue to believe she is alive somewhere.
Last week it was reported UK Home Office funding for Scotland Yard’s Operation Grange investigation into the disappearance will end this year.
The probe, opened in 2011, has so far cost more than €15million.
READ MORE: Madeleine McCann investigators uncover new evidence that 'heavily incriminates' suspect
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